• 한국소음진동공학회논문집
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• 제21권9호
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• pp.813-819
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• 2011

This paper predicted nonlinear dynamic responses of a cantilevered carbon nanotube(CNT) resonator incorporating the electrostatic forces and van der Waals interactions between the CNT cantilever and ground plane. The structural model of CNT includes geometric and inertial nonlinearities to investigate various phenomena of nonlinear responses of the CNT due to the electrostatic excitation. In order to solve this problem, we used Galerkin's approximation and the numerical integration techniques. As a result, the CNT nano-resonator shows the softening effect through saddle-node bifurcation near primary resonance frequency with increasing the applied AC and DC voltages. Also we can predict nonlinear secondary resonances such as superharmonic and subharmonic resonances. The superharmonic resonance of the nano-resonator is influenced by applied AC voltage. The period-doubling bifurcation leads to the subharmonic resonance which occurs when the nano-resonator is actuated by electrostatic forces as parametric excitation.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1999년도 전력전자학술대회 논문집
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• pp.650-654
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• 1999

In this paper, author describe the simulation results concerning the period doubling bifurcation route to chaos of DC/DC boost converter under current mode control to show that it is common phenomena on switching regulator when parameters are improperly chosen or continuously varied beyond the ensured region by system designer. Bifurcation diagrams of periodic orbits of inductor current and capacitor voltage of DC/DC boost converter are plotted with sampled data at moment of each clock pulse causing switching on. DC/DC boost converter studied on this paper is modelled by its state space equations as per switching condition under continuous conduction mode. Current reference signal and capacitance are chosen as the bifurcation parameters and those are varied in step for iterative calculation to find bifurcation points of periodic orbits of state variables.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 합동 추계학술대회 논문집 정보 및 제어부문
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• pp.294-297
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• 2002

We investigate the dynamics of a non-autonomous chaotic oscillator including an optocoupler that shows a periode-doubling and a chaos dynamics under any conditions of input circuit via experiments. Its characteristics was found to coincide input frequency components with output's. But, the relationship between input signals and output signals is different according to the amplitude of driving input voltage and circuit structure. Thus, this result can be applied to a wide variety of optical systems in the future.

• Progress in Superconductivity
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• 제10권2호
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• pp.74-78
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• 2009

Inter-grain nanobridges of the $MgB_2$ superconductor have been fabricated by focused-ion-beam(FIB) and their electrical transport properties were studied. The $MgB_2$ film was prepatterned into microbridges by a standard argon ion milling technique and then FIB-patterned into 100 nm$\times$100 nm bridges. Current-voltage characteristics showed a strong flux-flow type behavior at all temperatures with a trait of Josephson coupling near $T_c$. At low temperatures, the curves showed a two-step resistance-doubled transition with occasional hysteresis. The resistance-doubling transition is believed to be due to a two-channel flux-flow effect. The temperature-dependent critical current data showed $I_c(T){\propto}(1-T/T_c)^2$ near $T_c$, same as a normal barrier junction, and $I_c(T){\propto}(1-T/T_c)^{1.2}$ at low temperatures, similar to that of a film.

• 한국철도학회논문집
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• 제20권4호
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• pp.448-457
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• 2017

본 논문에서는 불연속 변조 기법을 이용한 고속철도 추진제어장치용 단상 PWM 컨버터에 대해 연구하였다. 기존 PWM 컨버터는 대 전력 특성으로 인해 스위칭 손실을 줄이기 위해 주파수 변조지수를 10 이하로 낮게 사용함에 따라 제어의 대역폭이 감소하고, 안정적인 역률 제어를 위해 추가의 보상 기법을 필요로 하는 등의 문제점을 가지고 있다. 이를 해결하기 위해 3상 PWM 인버터에서 사용하는 불연속 변조 기법을 단상 PWM 컨버터에 적용하였다. 제안한 방식은 옵셋 전압 기법을 활용하여 간단히 구현될 수 있으며 동일 스위칭 손실 대비 주파수 변조 지수를 2배 증가시켜 제어 특성을 향상시키고 스위치 간의 동특성도 동일하게 가져갈 수 있다. 100 kW급 PWM 컨버터에 대한 시뮬레이션을 통해 제안한 불연속 변조 기법에 대한 타당성을 검증하였다.